Transcript A Reflective Middleware Framework for Communication in

RFID Passive Tag
Architecture
Shariful Hasan Shaikot
Graduate Student
[email protected]
Oklahoma State University
Outline
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What is RFID tag
RFID System
Classification of RFID tag
Passive Tag
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Description of Different blocks of Passive Tag
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Antenna
Demodulator
Modulator
Power generator
Control Unit
Clock frequency block
Collision Detection
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What it is?
Main Concern
Physical Implementation
What passive tag must do?
How communication occurs?
Line Coding
Conclusion
References
What is RFID Tag
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A radio frequency tag (transponder) is an integrated
circuit containing –
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the RF circuitry and
the antenna
RFID System
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A basic RFID system consists of –
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a radio frequency tag (transponder) and
a reader (interrogator)
The reader sends out the RF signal carrying commands
to the tag.
Consequently, the tag responds with its stored data to be
authorized, detected, or counted.
RFID System
RFID
Classification of RFID Tag
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Three types of tag
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Active tag
Semi Passive Tag
Passive Tag
Another classification of tag
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read-write (R/W) - have an additional high voltage charge pump
circuitry that provides a higher power supply required for the write
operation in the memory cell
read-only (R/O) - animal identification, access control and
industrial automation
Passive Tags
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Passive tags have no
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On-tag power source - they make use of the power received from
the incoming RF signal to generate their own supply voltage
On-tag transmitter
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Passive tags have ranges of less than 10 meters
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Low cost
Passive Tags
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Main concern
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Power consumption – relies on electromagnetic fields for
power, energy is limited
Size – directly affects cost; the more silicon is used, the
more expensive the chip; Reducing the number of
components will minimize cost but causes high power
consumption, TRADEOFF!!!
Cost
Physical implementation of Tag
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A tag consists of an antenna
attached to an electronic circuit
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The antenna acts as a
transducer between
electromagnetic fields and
electric energy .
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A transmission line transfer this
energy to circuitry and vice versa
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The circuitry processes this
energy, stores it, uses it and
redirects it back through the
transmission line and antenna
Physical implementation of Tag
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The RF front end is responsible for
bidirectional interfacing between the
antenna and other functional blocks
of the tag
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In the RF front end, energy and data
are extracted from the input signal
and sent to power supply, clock
recovery and data processing
circuitry
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Over voltage protection is located in
the front end
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The type of memory used is Read
Only Memory (ROM) or Write Once
Read Many (WORM)
What Passive Tags must do?
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Passive tags must receive and rectify the incoming signal for the
extraction of energy and information
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It must store and manage the extracted energy to power the tag
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From the extracted information it must establish a clocking signal
with which to drive its digital circuitry
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Through this circuitry, it must process the information and make the
appropriate modulations of the incoming signal through backscatter
modulation
How communication occurs?
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Data between reader and tag are transmitted in half-duplex mode.
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The reader continuously generates a RF carrier wave, which powers
a passive tag when the tag is within its read range.
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The tag provides an acknowledgement to the reader by backscatter
and the detected modulation of the field indicates the presence of
the tag.
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The time taken for the tag to become fully functional is called the
setup time. After this time, the reader requests for read/write access
by sending appropriate instructions to the tag.
How communication occurs? (Contd…)
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The demodulator recovers the input data stream and passes control
logic circuitry deciphers the data to take corresponding action.
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After demodulation of the received instructions and handshaking,
the information stored in the tag is transmitted back to the reader by
backscattering.
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After all of the read/write operations are completed, the reader
acknowledges the successful completion of the communication and
the tag shuts off.
Architecture and Building Blocks of
Passive Tags
Antenna system
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Passive RFID tags are powered by the microwave signal received by
the antenna
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The tag needs a minimum signal level at its antenna terminals to
operate properly
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The tag will absorb some of the power to powering up itself and
detecting information
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It will scatter some power to transmit information back to the reader
Data Demodulation
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In the case of passive operation, there is a strict power constraint on
the tag’s design
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BER might be sacrificed for the simplicity of design and power
reduction in choosing the modulation scheme of the RFID system.
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In most of the passive RFID applications the data rate required is
relatively low
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Bandwidth efficiency may be traded for simplicity in a passive RFID
system
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Binary signaling should be preferred over M-ARY schemes.
Data Demodulation (contd…)
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Digital modulation schemes are preferred over the analog schemes
as they have better noise immunity and compatibility with the
developing technology of DSPs
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The information (from reader to tag) is conveyed through changes in
amplitude (ASK), phase (PSK) or frequency (FSK) of the carrier
signal.
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Another technique is Pulse Width Modulation (PWM) in which the
information is conveyed through variations of the width of pulse.
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The demodulation schemes are ASK, FSK, PSK and PWM.
Block Diagram of Demodulator
Description of Demodulator
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a preamplifier is used before the envelope detector to provide a DC
level shift to the input signal and perform amplification for better
detection.
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The envelope detector eliminates the carrier signal from the
received signal and provides the baseband modulating signals
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Due to the non-idealities (i.e. ripples and peak clipping effects) at the
output of the envelope detector, a Schmitt Trigger is used to
recover the clear digital pulse train.
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The output of the Schmitt Trigger serves as the clock at the data
rate for the rest of the processing circuitry
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The generated system clock is used to control the operation of the
integrator and sample the output of comparator properly.
Modulation
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Passive tags do not have enough power to generate a carrier and
modulate it, or to have a transmitter circuit.
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RFID applications use the Backscatter Modulation technique
whether it is ASK or PSK in transferring data from the tag
(transponder) to the reader (interrogator)
Backscatter modulation
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In the far-field, variation of the tag’s load impedance causes an
intended mismatch in impedance between the tag’s antenna and
load. This causes some power to be reflected back through the
antenna and scattered, much like the antenna is radiating its own
signal. The return scattered signal is detected and decoded by the
reader.
Backscatter communication between a
passive tag and the reader
Power generation block
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The reader continuously generates a RF carrier wave, which powers
a passive tag when the tag is within its read range.
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It makes use of RF-DC conversion and subsequent voltage
regulation to obtain the desired stable power supply.
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An enable signal is used to indicate the successful generation of the
power supply (VDD).
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A significant design challenge for the PG block is to maintain a
stable supply voltage
Power generation block
Power generation block
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The resonator/matching network is connected between the antenna and the
rectifier; and provides frequency selectivity and voltage gain to the system.
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The significant voltage gain enables the rectifier to overcome its dead zone
limitations.
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The intrinsic physical limitation on the operation of the devices
(e.g. the cut-in voltage of the diodes) is called the dead zone of
the device.
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The charge pump is used to boost the DC signal generated at the output of
the rectifier
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The charge stored across the load capacitor of the charge pump (Cload)
provides the unregulated supply voltage after the setup time.
Power generation block
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The reference circuit aims at generation of an independent
reference voltage to be used in voltage regulation
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The regulator is used to regulate the output of the charge pump and
provide a stable power supply (VDD) to the rest of the chip. It
minimizes the ripples and improves immunity to load variations
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The charge stored across the load capacitor of the charge pump
(Cload) provides the unregulated supply voltage after the setup time.
Control Unit block
Control Unit block
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The instruction format is represented by 12b:
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4b opcode
4b destination register address
4b source register address
The instruction set has 29 operations including an immediate
addressing mode
Control Unit block
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Registers in the CPU are organized as:
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A Program counter
An Immediate register
An I/O register
13 general purpose registers
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The demodulated data from RF block and modulation data from the
CPU are transferred through the I/O register
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Data transfer between memory (ROM/EEPROM) and register is
operated by LOAD/STORE instructions, in which the memory
address field refers to a register
Clock Frequency Control Circuit
Clock Frequency Control Circuit
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The clocking signal is used to drive the digital circuitry of passive
RFID tags
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In the data transmission, the lower frequency clock is selected since
fewer CPU executions are required
Line Coding
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For digital data transport line coding is often used.
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Line coding consists of representing the digital signal to be
transported, by an amplitude- and time-discrete signal, that is
optimally tuned for the specific properties of the physical channel
(and of the receiving equipment).
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The waveform pattern of voltage or current used to represent the 1s
and 0s of a digital signal on a transmission link is called line
encoding.
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NRZ, Manchester, RZ, Miller, PWM
Collision Detection
Collision Detection
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Anti-collision methods require the ability to detect collision
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Collision detection relies on coding scheme
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When simultaneously transmitted signals coded by certain schemes
add, they can not be resolved
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Manchester and other transition codes inherently allow this means
of collision detection
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NRZ and related level codes DO NOT allow this means of collision
detection
Collision Detection
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Other methods rely on modulation schemes
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Through FSK modulation in tag to reader transmission, readers can
detect “woobles” when multiple tag responds simultaneously
Conclusion
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Passive RFID tags can work on different frequency bands, ranging
from kHz to GHz.
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The choice of the frequency of operation affects the overall design of
the tag, since it controls the complexity, the cost, and the range of
operation
References
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Faisal A. Hussien, Didem Z. Turker, Rangakrishnan Srinivasan,
Mohamed S. Mobarak, Fernando P. Cortes and Edgar SánchezSinencio, “Design considerations and tradeoffs for passive RFID
tags”, VLSI Circuits and Systems II, Rosa, Proceedings of SPIE Vol.
5837, (SPIE, Bellingham, WA, 2005)
S. Masui, E. Ishii, T. Iwawaki, Y. Sugawara, K. Sawada, “A
13.56MHz CMOS RF Identification Transponder Integrated Circuit
With A Dedicated CPU”, IEEE International Solid-State Circuits
Conference, Digest of Technical Papers, Page:162 – 163, Feb.
1999.
The End
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